1. Field of the Invention
This invention relates generally to mooring systems for offshore structures such as platforms and vessels and in particular, to a device which supports the mooring chain in such systems.
2. Description of the Prior Art
FIG. 1 illustrates a prior art mooring line connector from U.S. Pat. No. 6,663,320 (published Dec. 16, 2003). The known connector allows the mooring line to rotate in two perpendicular planes relative to the offshore structure to which it is attached. The mooring line is connected using a rod and a latch mechanism. Adjustment of the length of the mooring line, which is often desired before and sometimes after installation of the mooring line, will have to take place before the rod is connected, most likely on board of another vessel.
FIG. 2 illustrates a prior art mooring line connector from UK Patent Application GB2351058 (published Dec. 12, 2000). This chain stopper provides two axes of rotation, and as a result reduced chain wear, but the construction is not designed to minimize so called out-of-plane bending, which occurs when the chain is under tension and one chain link (the captive link) is fixed by the chain stopper while the adjacent link below the captive link is allowed to rotate relative to the captive link. Also, during chain installation and tensioning, an uplift force is produced in the connector that must be resolved by bending the line of chain or by other means.
FIG. 3 illustrates a prior art mooring line connector from U.S. Pat. No. 7,926,436 (published Jul. 15, 2010). This chain support provides two axes of rotation, allows adjustment of the length of the mooring line and minimizes so called out-of-plane bending. The use of a trunnion block instead of a gimbal body forces the chain retainer mechanism to be located below the two axes of rotation which makes operation and maintenance of the chain retainer mechanism more challenging and requires the hawse pipe to be a load carrying member.
Identification of Objects of the Invention
A primary object of this invention is to provide a chain support in which fatigue damage due to out-of-plane bending is reduced.
Another object of this invention is to provide a chain support that allows rotation about two perpendicular axes, such that the maximum total rotation about the first axis is at least 90 degrees and the rotation about the second axis is ±15 degrees.
Another object of this invention is to provide a chain support that allows the upper end of the mooring line to be pulled up vertically through the assembly while at the same time allowing large vertical angle variations of the lower end of the assembly, without inducing objectionable vertical or lateral misalignment of the assembly with the mooring line.
Another object of this invention is to provide a chain support that allows adjustment of the mooring line length at any time by pulling in or letting out chain links with the capacity of latching into every other chain link.
Another object of this invention is to provide a chain support with an arrangement of components that minimizes the overall width of the assembly.
Another object of this invention is to provide a chain support with an integrated chain retainer guide that ensures that the chain maintains a straight line as it is pulled through the chain retainer mechanism.
Another object of this invention is to provide a chain support with an option of using either a dual chain retainer of the latch mechanism or a single chain retainer of the latch mechanism.